Tuning fork assembly



June 10, 1958 w. J. HOL-r, JR

TUNING FORK ASSEMBLY Filed Aug. 8, 1955 INVENTOR William J. Holi, Jr.

United States Patent() TUNING FORK ASSEMBLY William J. Holt, Jr.,Garland, Tex., assignor to Varo Mfg. Co., Inc.

Application August 8, 1955, Serial No. 526,894

Claims. (Cl. 310--25) My invention relates to the construction andarrangement of tuning fork assemblies, and more particularly to tuningfork assemblies of the type designed to function as elements of constantfrequency electronic oscillators.

An important problem in the construction of tuning fork assemblies hasalways been that of dealing with the adverse eiects of externalvibrations. In many instances in the prior art of which l am aware,substantial sacrilices have been made in the Q of tuning fork assembliesin order to circumvent theV problems of external vibrations. It has beenknown that solid base type forks have a high Q, if they are dynamicallybalanced. However the dynamic balancing has in itself presented seriousproblems. In addition to the problems above-mentioned, there have beenincreasing demands for tuning fork assemblies that are more rugged, moredependable, smaller in size, and susceptible to more economicalmanufacture.

It is accordingly an object of my invention to provide an improvedtuning fork assembly which shall obviate the above-mentioned problems.

It is another object of my invention to provide a tuning fork assemblyhaving high Q, and which is insensitive to effects of externalvibrations.

It is another object of my invention to provide a tuning fork assemblyutilizing a solid base type fork in an arrangement which allowsconvenient dynamic balancing of the fork.

' It is another lobject of my invention to provide a tuning forkassembly which is smaller in size and more economical to manufacturethan those heretofore available.

yThese and other objects are effected by my invention, as will beapparent from the following description, taken in accordance with theaccompanying drawings, in which:

Figure l is an elevational view of a completed tuning fork assembly;

Figure 2 is a center longitudinal section View of the tuning forkassembly; and

Figure 3 is an exploded view showing all of the parts of a completetuning fork assembly.

Referring now to the drawings and particularly to Figure 3, it will beseen that the tuning fork assembly comprises a base plug 11, a resilientring 13, a fork 15, a driving coil 17 and a pick-up coil 19, a two-piecefork and coil housing including identical matching left hand and righthand parts 21, 23, housing bolts 25 and nuts 27, a three-piece assemblyenvelope including a cap 29, and identical matching left hand and righthand skirts 31, 33.

The fork is of the solid base type made from a metal bar of rectangularcross-section. A deep U-shaped slot is formed in the bar so that themetal remaining at the slot sides constitutes the fork tines 35, 37. Thefork 15, has a pair of longitudinally aligned mounting holes 39, in itsbase portion.

The matching fork and coil housing pieces 21, 23, are made of moldednon-conducting material. The lower outside surface 41 of each housingpiece is cylindrical. The inner faces of the housing pieces arecomplementary, with the upper face portion in each case presenting aplane surface 43 and the lower portion having a projection 45 at oneside comprising a rst plane surface sloping having a single windingthereon.

ICS

downwardly and outwardly from the upper portion and a second planesurface extending downwardly and parallel to the upper portion. Theother side of the lower portion of the housing inner face has a rstplane surface extending downwardly and inwardly from the upper portion,and a second plane surface extending downwardly from the rst andparallel to the upper portion. A deep U-shaped groove 47 is formed inthe lower inside'surface of each housing piece. Thisgroove is centeredon the longitudinal axis of the respective housing piece and extends toapproximately the middle of the housing length. The depth of the grooveon the projection side is substantially equal to the width of the forkbase, while the width of the groove is substantially equal to the forkwidth. Each housing piece projection 45 carries a pair of `transverselyextending longitudinal bolt holes 49 which are located to register withthe bolt holes 39 in the fork base when assembled. The projection oneach housing piece has a recessed portion 51 on its outer surface forreceiving the bolt heads and nuts. The upper portion of each housingpiece has a plane outer face 53 parallel to the inner face. Each housingpiece has an additional surface 55 sloping downwardly and outwardly fromthe lower portion of the outer plane face 53. The last mentioned surface55 intersects the upper portion of the housing piece groove 47 so as toprovide a passage for the respective fork tine from the groove to thehousing outside upon assembly. The outer surface 57 of the upper portionof each housing piece between the upper inner and outer faces 43, 53 hasan inverted U-shaped contour. The thickness of the housing upper portionbetween the inner and outer upper faces is slightly less than one halfthe distance between the fork tines for a reason to be hereinafterexplained. The upper portion of the inner face of each housing piece hasa pair of cylindrical wells 59, 61 formed therein. The wells arecentered on the housing piece longitudinal axis, and have a diametersubstantially equal to the coil diameter and a depth substantially equalto one half the coil width.

There is a transversely extending hole 63 through the housing piece atthe center of each well having a diameter substantially equal to thecoil core diameter. Each housing piece 21, 23 has a pair of small holes65 communicating between the inner and outer upper faces of the piecefor a purpose to be hereinafter explained. Each housing piece has a pairof oppositely disposed inwardly extending dimples 67-69 at the marginaledges of their outer surfaces. These dimples are located longitudinallyof the housings at a point corresponding to the center of gravity of thefork, housing, and coil assembly for a purpose to be hereinafterexplained. Each housing piece 21, 23 has a small groove 71 in its innerface which communicates with both coil wells and provides a channel forthe coil leads 73 from the coils out through the bottom of the housingpieces, and also a passage for filler material.v

The drive coil 17 and pick-up coil 19, which are identical, are in theform of short cylindrical bobbins, each The coil cores 75, 77 arecylindrical pins of magnetic material which extend through registeringholes 63 in the housing wells, 59, 61.

The envelope skirts 31, 33 are identical halves of a thin metal cylindereach having an inwardly extending dimple '7 9 in its upper portion.

The resilient ring 13 is simply a heavy rubber band designed to tclosely over the cylindrical end of the coil and fork housing uponassembly. The base plug 11 is a metal ring 81 having a disc 83 ofnon-conducting ,marte-V rial fixed to its inner periphery with plug pinsS5 xed to the disc. The base plug outer diameter is such that the plugwill t snugly inside the lower end portion of the envelope skirts uponassembly. The cap 29 isV a es hollow thin metal cylinder with one endrounded and closed.

To assemble the device, the pick-up coil 19 is placed in the upper well59 of one housing piece 23, while the drive coil'l is placed in thelower well 6l of the other housing piece 2l and the coil leads 73 arelaid in their respective housing channels 7l to extend from the bottomthereof. The housing pieces 21, 23 are then tted together and the coilcore pins 75, 77 inserted. Next, the fork is inserted so that its tines35, 37 extend up through the appropriate housing openings with the innerfaces of the tines closely adjacent the respectiveouter plane faces 53of the housing pieces. The bolts Z5 are then passed through theregistered holes 49 in the housing piece projections 45 and the forkbase and secured by the nuts 27.

Next, impregnating material is injected through the small holes 65 inthe housing piece upper portions until the coil' and fork housing iscompletely filled. The impregnating material hardens so that the coils,their cores, the fork base andthe bolts and nuts arc all held rigid, andthe entire assembly is completely sealed. Next, the resilient ring 13 isslipped on the cylindrical portion of the housing and centered onV thehousing dimples 67, 69. Next, the envelope skirts 3l, 33 are assembledon the housing with their inwardly extending dimples 79 centered on theresilient ring 13 and registered with corresponding dimples 67, 69 onthe housing. Then the cap 29 is placed over the upper end of the housingandV down over the skirts 31, 33, making a tight friction t over theskirtsV and clamping them together in matched relation. Then the coilleads 73 are connected to appropriateV base plug pins S5, and the baseplug 11 is inserte inside the bottom portion of the skirts 3l, 33,making a snug t therewith. The assembly is completed by solderingthebase plug ring 8l to the envelope skirts.

It is evident that the arrangement and construction of the tuning forkassembly of my invention provides a large measure of compactness andruggedness. In addition, the' coilV and fork housing assembly isshockmounted at' its center of gravity by means of the dimples on thehousing Vand the envelope skirts, in co-operation with the resilientring. This means that external vibrations have minimum effect on thefork. Furthermore, the rco-axial construction of the device with thecoils between the fork tines not only lends itself to small size andcompactness, but also balances out the effects of external vibrations.Thus, if one fork tine is caused by an external shock to vibrate furtheraway from one side of the coils than normal, the other fork tine will atthe same time vibrate closer to the other side of the coils than normalby a like amount, thereby balancing out the adverse eect. Anotherimportant attribute of the arrangement and construction of my inventionis that it permits precise and convenient dynamic balancing of the forkunder actual operating conditions with the fork and coils and theirhousing completely assembled and sealed in final form. This is truebecause the fork tines are exposed in the final assembly so that testequipment can be readily applied and the metal necessary for precisedynamic balance can be readily removed from the fork tines. A furtheradvantage of my construction and arrangement is that it lends itself tomore economical manufacture. it has been found in actual practice thatassemblies embodying my invention can be manufactured forjas Ylittle asone half the cost per unit of assemblies heretofore manufactured. A

While I have shown my invention in only one form, it will be apparent tothose skilled in the art that it is not soY limited, but is susceptibleof vario1 s changes and modifications without departing from the spiritthereof.

I claim:V

l. A tuning fork assembly comprising, a soiid base type'tuning forkhaving tines, a drive coil, a pick-up coil,'a housing presenting acylindrical outer surface at ,4 itslower portion tapering rto spacedparallel plane outer surfaces at its upper portion, a cavity in thelower inside portion of said housing for receiving the base of said forkwith the fork tines extending exteriorly of the housing with their innerfaces parallel to and closely adjacent said spaced parallel housingouter surfaces, cavities in the upper portion of said housing centeredon the housing longitudinal axis for receiving said coils, means forrigidly securing the base of said fork and said coils within saidhousing, and means for sealing the assembly.

2. A tuning fork assembly comprising, a solid base type tuning forkhaving tines, a drive coil, la pick-up coil, a housing presenting acylindrical outer surface at its lower portion tapering to spacedparallel plane outer surfaces at its upper portion, a cavity in thelower inside portion of said housing for receiving the base ot' saidfork with the fork tines extending exteriorly of the housing with theirinner faces parallel to and closely adjacent said spaced parallelhousing outer surfaces, cavities in the upper portion of said housingand centered on the housing longitudinal axis for receiving said coils,means for rigidly securing the base of said fork and said coils withinsaid housing, and means for shock mounting the assembly at its center ofgravity. Y

3. A tuning fork assembly comprising a solid base type tuning forkhaving tines, a drive coil, a pick-up coil, a housing presenting acylindrical outer surface at its'lower portion tapering to spacedparallel plane outer surfaces at its upper portion, a cavity in thelower inside portion of said housing for receiving the base of said forkwith the fork tines extending exteriorly of the housing with their innerfaces parallel to and closely adjacent said spaced parallel housingouter surfacesLcavities in the upper portion of said housing andcentered on the housing longitudinalV axis for receiving said coils,means for rigidly securing the base of said fork and said coils withinsaid housing, inwardly extending dimples disposed on opposite sides ofsaid housing outer surface at the assembly center of gravity, aresilient ring girding said housing and centered over the housingdimples, a three piece envelope comprising a pair of identicalsemi-cylindrical metal skirts each having all inwardly extending dimplecentered at its upper portion, a cylindrical cap closed at one end, saidskirts being assembled on said i housing cylindrical portion andextending downwardly therefrom with the dimples registered overrespective housing dimples, the cap covering the upper portion ofsaidhousing and making a friction tit over the upper portions of saidskirts, a base plug making a frictioniit inside the lower portions ofsaid skirts andhaving plug piece, and electrical connection between saidcoils and said pins.

4. A housing for a tuning fork assembly, said housing comprising a pairof substantially identical matching pieces, each piece having acylindrical outer surface at its lower portion tapering to a planesurface atits upper portion,1a plane surface at the piece inner facewith an outwardly extending projection a-t one side of the lower portionand an inwardly extending recess at the other side, a deep U-shapedVgroove centered on the inner face and extending upwardly between saidprojection and recess to intersect the tapered portion of ythe housingpiece outer surface forming an opening through the housing, a cavity inVsaid lower portion of said housing piece inner face and centered' on itslongitudinal axis for receiving tuning fork base, a pair of transverselyextending cylindrical openings being ywe'lls'in said housing piece forreceiving coil cores, a groove in said housing piece inner facecommunicating between said wells and the lower end of said 'housingpiece, and means forV holding said housing pieces in matched rigidrelation. Y

5. A tuning fork assembly comprising a tuning fork having a base andtines, a drivecoil, 'a pickup coil and a housing, said housing havingVupper and lower portions, said upper' portion adapted'to hold' saidcoils firmly between said tuning fork tines so that the said tinesextend exteriorly of said upper portion of said housing and said lowerportion adapted to hold the said tuning fork base tirmly in said lowerportion of the housing.

6. A tuning fork assembly comprising a tuning fork having a base andtines, a drive coil, a pick up coil and a housing, said housing havingupper and lower portions, said upper portion adapted to hold said coilsfirmly between said tuning forli ltines so that the said tines extendexteriorly of said upper portion of said housing and said lower portionadapted to hold the said tuning fori; base rmly in said lower portion ofthe housing, said housing being comprised of a pair of matched housingpieces which join together to make a unitary housing.

7. A tuning fork assembly comprising a tuning fork having a base andtines, a drive coil, a pick up coil and a housing, said housing havingupper and lower portions, said upper portion adapted to hold said coilstirmly oetween said tuning fork tines so that the said tines extendexteriorly of said upper portion of said housing and said lower portionadapted to hold the said tuning fork base rmly in said lower portion ofthe housing, said houdq ing being comprised of a pair of matched housingpieces which join together to make a unitary housing and means for shockmounting the assembly to minimize external shock vibrations.

8. A tuning fork assembly comprising a tuning fori; having a base andtines, a drive coil, a pick up coil and a housing, said housing havingupper and lower portions, said upper portion adapted to hold said coilsfirmly between said tuning fork tines so that the said tines extendexteriorly of said upper portion of said housing and said lower portionadapted to hold the said tuning fork base tirrnly in said lower portionof the housing and means for shock mounting the assembly to minimizeexternal shock vibrations.

9. A tuning fork assembly comprising a tuning fori; having a base andtines, a drive coil, a pick up coil and a housing, said housing havingupper and lower portions, said upper portion adapted to hold said coilsiirrnly between said tuning fork tines so that the said tines extendexteriorly of said upper portion of said housing and said lower portionadapted to hold the said tuning fork base lirmly in said lower portionof the housing, an enclosure for said tuning fork assembly and means toshock mount said tuning fork assembly in said enclosure.

10. A tuning forli assembly comprising, a tuning fork having a base andtines, a drive coil, a pick up coil, a housing presenting a cylindricalouter surface at its lower portion tapering to spaced parallel planeouter surfaces at its upper portion, a cavity in the lower insideportion of said housing for receiving the base of said fork with thefork tines extending exteriorly of the housing with their inner facesparallel to and closely adjacent said spaced parallel housing outersurfaces, said upper portion having a cavity for receiving said coils,means for rigidly securing the base of said fork and said coils withinsaid housing, and means for sealing the assembly.

11. A tuning fork assembly comprising, a tuning forli having a base andtines, a drive coil, a pick up coil, a housing presenting a cylindricalouter surface at its lower portion tapering to spaced parallel planeouter surfaces at its upper portion, a cavity in the lower insideportion of said housing for receiving the base of said fork with thefork tines extending exteriorly of the housing with their inner facesparallel to and closely adjacent said spaced parallel housing outersurfaces, the upper portion 0f said housing having a cavity forreceiving said coils, means for rigidly securing the base `of said forkand said coils within said housing, and means for shock mounting theassembly.

12. A tuning for assembly comprising tuning fork having a base andtines, a drive coil, a pick up coil, a housing presenting a cylindricalouter surface at its lower portion tapering to spaced parallel planeouter surfaces at its upper portion, a cavity in the lower insideportion of said housing for receiving the base of said fork with tl efork tines extending exteriorly of the housi' wit` their inne* races ptallel to and closely adjacent sp ed parallel housing outer surfaces,said upper portion of said housing having a cavity for receiving saidcoils, means for rigidly securing the base of said fori; and said coilswithin said housing, inwardly extending dimpies disposed on oppositesides of said housii 'f o ico at substantially the assembly center of gavity, a resilient ring girding said housing and centered over thehousing dimples, a three piece envelope comprising a pair of identicalsemi-cylindrical metal skirts each having ail inwardly extending dimplecentered at a cylindrical cap closed at one end, ts being assembled onsaid housing cylindrical portion and extending downwardly therefrom withthe dimples reg, ered over 'respective housing dimples, the cap coveringthe upper portion of said housing and maliing a friction tit over theupper portions of said skirts, a base plug making a friction tit insidethe lower portions of said skirts and having ping piece, and electricalconnection between said coils and said pins.

13. A housing for a tuning assembly, said housin' compi ,ing a pair otsuo l ;ntiaily identical matching pieces, caca piece having acylindricai outer surface at its tower portion tap ng to a plane surfaceat its upper portion, a pla surfae tl iecc inner tace with outwardiyextendin one side of the lower portion i ing recess at the other side, adeep U-so ntered on the inner face and extending u ,v between saidprojection and recess to intersect the tapered portion of the housingpiece outer surface forming an opening through the housing, a cavity insaid -wer 'ortion of said housing piece inner and centered on itslongitudinal axis for recei g tuning fork base, a cavity in said upperportion cf housing piece for receiving coil cores, a groove in saidhousing piece inner face communicating between said upper portion cavityand the iower end cf said housing piece, and means for holding saidhousing pieces in matched rigid relation.

14. A tuning fori: assembly comprising a tuning fori housing, a tuningfork having a base and spaced legs extending therefrom, a pick up coil,a driving coil, said he* ing having an upper portion adapted to holdsaid coils between the legs of the tuning fork and a lower portion tohold the tuning fork base, a shock absorbing means positioned about saidtuning fork housing and enclosure adapted to enclose said tuning forlihousing and said shock absorbing means whereby the tuning forli housingand tuning fork are effectively protected from external shock vibrationsto the enclosure.

l5. A tuning fork assembly comprising a tuning fork housing, a tuningfork having a base and extending tines, a pick up coil, a driving coil,said housing having an upper portion adapted to hold said coils betweenthe tines of the tuning fork, a lower portion to hold the tuning forlihase and a plurality of indentations on the outer periphery of saidhousing, a shock absorbing means positioned about said tuning forlihousing, a, plurality of A icing plates having protuberances adapted toprovide a xed relationship of the said plates and fork housing by virtueof the said indentations and an en closure adapted to enclose saidspacing plates and said tuning fori: housing whereby external shockvibrations to the enclosure are minimized in the tuning fork.

References tCited in the tile of this patent UNlTED STATES PATENTS

